1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head that irradiates near-field light (NF light) to a magnetic recording medium, decreases an anisotropic field of the magnetic recording medium and records data, a head gimbal assembly using the head and a magnetic recording device.
2. Description of the Related Art
In the field of magnetic recording using a head and a medium, further performance improvements of thin film magnetic heads and magnetic recording media have been demanded in conjunction with a growth of high recording density of magnetic disk devices. Currently, composite type thin film magnetic heads are widely used for the thin film magnetic heads. The composite type thin film magnetic heads have a configuration in which a magnetoresistive (MR) element for reading and an electromagnetic conversion element for writing are laminated.
The magnetic recording medium is a discontinuous medium in which magnetic grains are aggregated, and each of the magnetic grains has a single magnetic domain structure. In this magnetic recording medium, a single recording bit is configured with a plurality of magnetic grains. Therefore, in order to increase recording density, asperities at a border between adjacent recording bits need to be reduced by decreasing the sizes of the magnetic grains. However, reducing the magnetic grains in size leads to a decrease in the volumes of the magnetic grains, and thereby drawbacks occur in that thermal stability of magnetization in the magnetic grains decreases.
As a countermeasure against this problem, increasing magnetic anisotropy energy Ku of magnetic grains may be considered; however, the increase in Ku causes an increase in an anisotropic magnetic field (coercive force) of the magnetic recording medium. On the other hand, the upper limit of the writing magnetic field intensity of the thin film magnetic head is substantially determined by saturation magnetic flux density of a soft magnetic material configuring a magnetic core in the head. As a result, when the anisotropic magnetic field of the magnetic recording medium exceeds an acceptable value determined by the upper limit of the writing magnetic field intensity, it becomes impossible to write to the magnetic recording medium. Currently, as a method to solve such a thermal stability problem, a so-called thermally-assisted magnetic recording method has been proposed in which, while a magnetic recording medium formed of a magnetic material with large Ku is used, under a state where the anisotropic magnetic field is reduced by heating the magnetic recording medium, a writing magnetic field is applied and the writing of information is performed.
In the thermally-assisted magnetic recording method, a method that uses a near-field light probe, or so-called plasmon-generator having a metal piece that generates near-field light from plasmon excited by laser light, is generally known.
The conventionally-proposed magnetic recording head equipped with a plasmon-generator has a configuration where a magnetic pole that generates the writing magnetic field is established closer to the trailing side than a near-field light generating portion of the plasmon-generator, and a waveguide that propagates light to be opposed to the plasmon-generator, is closer to the leading side than the near-field light generating portion. The plasmon-generator is coupled with light propagating in the waveguide in a surface plasmon mode to excite the surface plasmon, and generates NF light at the near-field light generating portion because the surface plasmon propagates through the plasmon generator. Then, the magnetic recording medium is heated by the NF light generated at the near-field light generating portion of the plasmon-generator, and, after the anisotropic field of the magnetic recording medium is reduced, the writing magnetic field is applied and information is written.
In such a magnetic recording head, when the NF light is generated at the plasmon-generator to reduce the anisotropic field of the magnetic recording medium, the vicinity of the near-field light generating portion of the plasmon-generator is also heated by the NF light. Due to the heating, the vicinity of the near-field light generating portion of the plasmon-generator configured with metal is likely to be deformed. If the plasmon-generator is deformed, it becomes difficult to generate NF light that can effectively heat a magnetic recording medium.
In order to solve such problem, although a metallic material with high thermostability (for example, metallic materials or alloy materials with a high melting point) may be used to configure the plasmon-generator, the coupling efficiency to couple light that propagates through a waveguide in the surface plasmon mode is decreased and generating efficiency of the NF light is decreased. Consequently, a metallic material that has high thermostability and that can efficiently generate the NF light is required to configure the plasmon-generator.
In the thermally-assisted magnetic recording head, it is desirable to increase a ratio of temperature of a magnetic recording medium (temperature of a recording layer of a magnetic recording medium) to a temperature in the vicinity of the near-field generating portion (head surface temperature) upon irradiating NF light (MH ratio).